2526 - Re-Irradiation of Anaplastic Meningioma. Local Control Factors and Toxicity Report.

O. Haisraely¹, M. SIvan², and Y. Lawrence³; ¹Chaim Sheba Medical Center, Ramat Gan, Israel, ²Sheba Medical Center, Ramat gan, Israel, ³Radiation Oncology Department, Sheba Medical Center, Ramat Gan, Israel

Purpose/Objective(s): Anaplastic meningioma constitutes 1%–2% of all meningiomas and presents a particularly aggressive clinical course with poor survival outcomes. The 3-year progression rate for these tumors, even after gross total resection and adjuvant radiation, is 59.2%, while the overall survival is 78.6%. The optimal management of anaplastic meningioma in the recurrent setting is not well defined, with almost no literature on the toxicity of re-irradiation in this clinical context. In this multi-institutional analysis, we evaluate the outcomes of re-irradiation in the setting of recurrent anaplastic meningioma, considering both local control and overall survival, as well as toxicity. Materials/

Methods: After obtaining IRB approval, we conducted a retrospective data review of patients treated with re-irradiation for recurrent/progressive anaplastic meningioma. These patients were treated at three of the largest medical centers between 2017 and 2023.
Results: A total of 34 cases of recurrent anaplastic meningioma, who received a 2^nd course of radiation, were analyzed. The average age was 57.2, and 55.8% were females. Most of the patients (70%) were diagnosed based on the mitotic rate, with 10 patients having CDKN2A homozygote deletions. In the recurrent/progression setting, 73% of the cohort underwent a 2^nd surgery (Simpson > 3). All patients received a 2^nd course of RT with a median dose of 48.8Gy. 35.3% received concomitant Bevacizumab.The median follow-up was 25 months from the 2^nd radiation (3-83 months). Local control was 64%. The median progression free survival was 23 month vs 11 month for those who had 2nd suregry and those who didnt, respectivily. (p=0.02) Among the patients who received a 2^nd RT dose above 50Gy (EQD2) the miedian progreesion free survival has not reached, in comparison to 12 month in those who recieved a dose lower than 50Gy (p<0.001). No significant variable differences were observed between those who received more than 50Gy versus those who didn’t Having CDKN2A homozygote deletion increased the hazard ratio for local failure by 3.6 (1.2-12.3, p=0.021). In a multivariable analysis, the total dose remained significant for local control (p=0.038), while 2^nd surgery did not impact local control (p=0.10). Toxicity 20% symptomatic radiation necrosis (RN) rate. A total dose above 120Gy combined increased the risk for RN (HR-2.4). There were no cases of symptomatic radiation necrosis among patients who received concomitant Bevacizumab.
Conclusion: Anaplastic meningioma has a poor prognosis. Re-irradiation seems plausible but confers a 20% risk of symptomatic RN, especially if the combined dose is above 120GY. Resection, total dose, and CDKN2A status are important considerations for local control in the recurrent setting. In multivariable analysis, the total dose delivered seems to be more important than having a 2^nd surgery for local control. The use of concomitant Bevacizumab doesn’t impact local control but may reduce the risk of RN.